Circuit breakers, both single and multi-phase circuit breakers, typically include a lever or other device for manually operating the circuit breaker. Frequently, it is desirable that the lever be operated through the use of a mechanical interface, such as a direct mount rotary handle operating mechanism having a handle that may be manually operated, wherein the handle mechanism is of the type that is directly mounted to the circuit breaker.
In operation, the handle mechanism moves the circuit breaker lever to its various operative positions. This includes an “ON” position, an “OFF” position and a “RESET” position. In some instances, it is necessary to lock the handle mechanism in the OFF position so as to safeguard personnel working on associated equipment. However, when the electrical contacts of the circuit breaker have become welded closed, usually as a result of a short circuit condition, locking the handle mechanism in an OFF position would create a dangerous and inappropriate condition since a user would believe that the circuit breaker is in the OFF (electrical contacts open) condition, when in fact the electrical contacts are welded closed.
Conventional handle mechanisms include a locking portion that will not enable locking of the handle when the contacts are welded together. This is commonly referred to as “Suitable for Isolation” or “Positive OFF”. In addition, the handle will return to indicate the ON position when the handle is released. These are safety features that indicate to the user that the contacts are welded and that substantially reduce the likelihood that others working on the equipment would mistakenly believe that the contacts are open.
However, conventional handle mechanisms rely on the proper positioning of the handle as a way of ensuring that it will not lock during Positive OFF. The disadvantage of such mechanisms is, that with wear, the position of the handle mechanism approaches the locked position. Further, such mechanisms rely on the force limits set by standard specifications, such as those set by the International Electrotechnical Commission (IEC), in order to ensure the handle cannot be locked.
Thus there is a need for a direct mount rotary handle operating mechanism for a circuit breaker that will prevent the handle from being locked in an OFF position when the electrical contacts of the circuit breaker are in fact closed, such as in a welded closed condition.